1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording for use to write data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that includes a write shield.
2. Description of Related Art
The recording systems of magnetic recording devices such as magnetic disk drives include a longitudinal magnetic recording system in which the magnetization of signals is directed along the plane of a recording medium (the longitudinal direction), and a perpendicular magnetic recording system in which the magnetization of signals is directed perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on the top surface of a substrate. The write head unit includes a main pole for producing a write magnetic field in a direction perpendicular to the plane of the recording medium.
A magnetic head for use in a magnetic disk drive is typically incorporated in a slider. The slider has a medium facing surface configured to face a recording medium. A main pole has an end face located in the medium facing surface. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is configured to slightly fly over the surface of the recording medium by means of an airflow that comes from the leading end into the space between the medium facing surface and the recording medium. The recording medium includes a magnetic recording layer. Tracks are concentrically formed in the magnetic recording layer. The tracks are the area of the magnetic recording layer on which data is to be written.
Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs depending on the position of the magnetic head across the tracks.
Particularly, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, there may occur the phenomenon that signals already written on one or more tracks in the neighborhood of a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. Unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). Unwanted erasure is noticeably encountered upon occurrence of a skew. For enhancement of recording density, it is necessary to prevent unwanted erasure.
A known technique for preventing unwanted erasure induced by a skew is to shape the main pole such that its end face located in the medium facing surface has a width that decreases with decreasing distance to the top surface of the substrate. Further, a known technique for preventing the skew-induced unwanted erasure and enhancing the recording density is to provide a wrap-around shield and a gap section, the wrap-around shield being a write shield having an end face that is located in the medium facing surface and surrounds the end face of the main pole, the gap section separating the wrap-around shield from the main pole. These techniques are disclosed in, for example, U.S. Pat. Nos. 8,289,649 B2 and 8,472,137 B2, and U.S. Patent Application Publication Nos. 2012/0147499 A1 and 2013/0242431 A1.
The wrap-around shield includes a leading shield, first and second side shields, and a trailing shield. The leading shield has an end face located in the medium facing surface at a position on the leading side of the end face of the main pole. The first and second side shields have two end faces located in the medium facing surface at positions on opposite sides of the end face of the main pole in the track width direction. The trailing shield has an end face located in the medium facing surface at a position on the trailing side of the end face of the main pole.
The gap section includes a leading gap section for separating the leading shield from the main pole, first and second side gap sections for separating the first and second side shields from the main pole, and a trailing gap section for separating the trailing shield from the main pole.
The wrap-around shield has the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, and thereby preventing the magnetic flux from reaching the recording medium. A magnetic head provided with the wrap-around shield is able to prevent unwanted erasure and provide further enhanced recording density.
The position of an end of a record bit to be recorded on the recording medium is determined by the position of the trailing-side edge (hereinafter referred to as the top edge) of the end face of the main pole in the medium facing surface. Accordingly, what are important for enhancing the writing capability of the write head unit include: high write magnetic field strength at the top edge or in the vicinity thereof; and a large gradient of change in the write magnetic field strength at the top edge or in the vicinity thereof in the distribution of the write magnetic field strength in the direction in which the tracks extend. High write magnetic field strength at the top edge or in the vicinity thereof contributes to the enhancement of overwrite property. A large gradient of change in the write magnetic field strength at the top edge or in the vicinity thereof contributes to the reduction of bit error rate.
A magnetic head provided with a wrap-around shield suffers from the problem that when a large amount of magnetic flux leaks from the main pole to the wrap-around shield, particularly to the leading shield and the first and second side shields, there occurs reductions in the write magnetic field strength and the aforementioned gradient of change at the top edge of the end face of the main pole or in the vicinity of the top edge, and the writing capability is thereby degraded.
U.S. Patent Application Publication No. 2011/0262774 A1 discloses a magnetic head including a main pole, first and second side shields, a trailing shield, first and second side gap sections, and a trailing gap section. In this magnetic head, each of the first and second side gap sections includes a portion that increases in thickness with increasing distance from the medium facing surface. However, this magnetic head includes no leading shield and no leading gap section. This magnetic head is thus unable to suppress, on the leading side of the end face of the main pole, the spread of the magnetic flux produced from the end face of the main pole.
U.S. Patent Application Publication No. 2012/0147499 A1 discloses a structure in which the leading gap section has a greater thickness in the medium facing surface than each of the first and second side gap sections. However, it is difficult with this structure alone to suppress leakage of magnetic flux from the main pole to the leading shield and the first and second side shields.
U.S. Patent Application Publication No. 2013/0242431 A1 discloses a structure in which the leading gap section has a greater thickness in the medium facing surface than each of the first and second side gap sections and the thickness of each of the first and second side gap sections increases with decreasing distance to the leading shield, and further discloses a structure in which the thickness of the leading gap section decreases with increasing distance from the medium facing surface. Such a structure, however, is prone to leakage of magnetic flux from the main pole to the leading shield at a location away from the medium facing surface.